1. Field of the Invention
The present invention relates to a method for inspecting magnetic characteristics of thin film magnetic heads, more particularly, to a method for inspecting thin film magnetic heads arranged in a row bar.
2. Description of the Related Art
Conventionally, thin film magnetic heads are manufactured by the following steps. First, a stack that includes a magnetic field sensor (a read head portion) and a write head portion is formed on a substrate in the wafer process. Next, the wafer is diced and separated into row bars. A plurality of sliders is disposed in each row bar along the longitudinal direction thereof, and each slider is provided with a thin film magnetic head that is formed in the wafer process. A row bar serves as a work unit in a lapping step for forming an air bearing surface. When lapping is completed, the row bar is separated into individual sliders, each of which is then assembled into a head gimbal assembly and mounted on a hard disk drive in the final process.
The thin film magnetic head, prior to being finished as a slider and being sent to a subsequent process, undergoes an inspection of magnetic characteristics and other tests. Conventionally, sliders are separately attached to a dedicated inspection apparatus, called the spin stand, and inspected one by one. This method enables sliders to be inspected in the same environment as in a state in which the sliders are actually mounted on hard disk drives, but is disadvantageous as regards the efficiency of the inspection. Accordingly, there has been proposed a method for collectively inspecting sliders that are mass-produced.
Japanese Patent Laid-Open Publication No. 150264/94 discloses an inspection method called quasi-static test (QST). The test, which is performed prior to the final assembling of hard disk drives, simulates an actual environment. Specifically, an alternating magnetic field (refers to an alternately changing magnetic field) that is generated by a magnetic field generator is applied from the outside, instead of a magnetic field emitted from a recording medium, in order to collectively measure and evaluate various magnetic characteristics of a plurality of sliders arranged in a row bar. A Helmholtz coil is used as the magnetic field generator. Application of high-frequency alternating current to the Helmholtz coil causes the Helmholtz coil to generate an alternating magnetic field. The row bar is placed in front of the Helmholtz coil so that an alternating magnetic field is applied to magnetic field sensors. The alternating magnetic field simulates a varying magnetic field, which corresponds to signal “0” and “1”, that the magnetic field sensors receive from a rotating magnetic disk in an actual environment. A sense current is generated to flow in the magnetic field sensors by means of probes. In accordance with a change in the magnetic field, the output voltage of the magnetic field sensor changes due to magnetoresistance effect. In this way, the relationship between the external magnetic field and the signal output (output voltage) can be obtained. The data that are obtained are used to evaluate the magnetic characteristics of the magnetic field sensors and to prevent defective sliders from being sent to a subsequent process.
In recent years, ultra-high recording density of hard disk drives has been promoted. The ultra-high recording density essentially requires ultra-high linear recording density. The ultra-high linear recording density means an increase in the frequency of an alternating magnetic field that is applied to a thin film magnetic head. Accordingly, it is preferable that thin film magnetic heads that realize the ultra-high linear recording density be inspected under the environment of an alternating magnetic field having an ultra-high frequency. However, in a conventional Helmholtz coil, there is a limitation to an increase in the frequency of an alternating magnetic field because of the characteristics of the device. Frequencies in the order of several hundred kilohertz are within the capability of the Helmholtz coil, but frequencies higher than 1 megahertz are difficult to achieve. However, alternating magnetic fields in the order of several megahertz are found in the actual environment of hard disk drives. Thus, it has already been difficult to completely simulate the actual environment by a conventional QST. Use of a spin stand may realize such high frequencies, but will lead to inefficiency in the inspection.